With iThemes Security Pro, you can add a reCAPTCHA to your registration and log in forms in iThemes Exchange.
Adding the reCAPTCHA is easy and gives you added protection against spam registration attempts and brute force login attempts.
To start using reCAPTCHA, from your WordPress dashboard navigate to iThemes Security>Pro Tab and go to the reCAPTCHA section.
After you enable the feature, you will need to get Site and Secret Keys from Google. From your iThemes Security dashboard, you can click the blue Google reCAPTCHA link to obtain your keys.
To get the keys needed to activate reCAPTCHA just go to google.com/recaptcha and log in with your Google credentials. Then you will register a new site.
Once you have set this up in iThemes Security Pro, you will need to go to Exchange > Add-ons and enable the iThemes Security add-on there.
Once this has been configured, the reCaptcha will show on both your registration and log in forms.